1. Field of the Invention
The present invention relates to a mobile communication system and, more particularly, to a reception/transmission mode switching method for a transceiver of a mobile terminal in a TDD-based mobile communication system.
2. Description of the Related Art
A time division synchronous CDMA (TD-SCDMA) is a third-generation (3G) mobile communication standard being developed by the initiative of China approved as a third generation mobile communication standard together with WCDMA and CDMA-2000 of the ITU. The TD-SCDMA aims at increasing channel capacity and effective resource management by combining merits of time division duplex (TDD) and uplink synchronization of CDMA with a smart antenna.
In a TDD-based communication system such as the TD-SCDMA, transmission and reception channels are separated in the time domain. A mobile terminal operates reception/transmission modes in alternate steps by switching the mode of a transceiver.
FIG. 1 illustrates the construction of an RF transceiver of a general TD-SCDMA terminal, including a transmission module 15, a reception module 12, and a switch 17 for selectively connecting the reception module 12 and the transmission module 15 to an antenna (ANT). The switch 17 connects the antenna to the transmission module 15 or to the reception module 12, according to a reception/transmission synchronization signal received from a base station.
When the mobile terminal is switched to a reception mode such that the reception module 12 is connected to the antenna, the reception module 12 down-converts a signal received through the antenna to a baseband signal, and the baseband signal is converted into a digital signal by a baseband modem 19.
Meanwhile, when the mobile terminal is switched to the transmission mode such that the transmission module 15 is connected to the antenna, the transmission module 15 converts a digital signal from the baseband modem 19 into an analog signal. The converted analog signal is up-converted into a radio frequency signal in the baseband by the transmission module 15 and is then transmitted through the antenna. Usually, the transmission module 15 and the reception module 12 automatically enter a sleep/standby mode based on a transmission/reception mode switching signal, in order to reduce power consumption.
In a symmetrical TD-SCDMA system, a high speed data rate of 2 Mbps is supported. Uplink and downlink time channels are equally provided in time domain such that the transmission/reception mode conversion of the mobile terminal occurs very frequently. Accordingly, switching control of the power mode of the reception and transmission module 12 and 15 becomes complex.
FIG. 2 illustrates a frame format in a TD-SCDMA system. As shown in FIG. 2, the radio frame has a length of 10 ms and consists of two sub-frames. Each sub-frame is split into a plurality of time slots. An upward time slot TS3 and a downward time slot TS4 are discriminated by a switching point. A minimum guard period (GP) at the switching point is 16 chips (about 12.5 μs). Therefore, the transmission/reception mode switching of the mobile terminal should be performed during the GP, i.e., 16 chips.
Unfortunately, with the current technique, it is difficult to implement a reception/transmission module performing a reception/transmission mode switching in a time period less than 12.5 μm. And, even if the reception/transmission module having a mode switching time less than the minimum guard period is developed, it is not cost effective to implement a high speed reception/transmission module to a TD-SCDMA terminal. A method and system is needed to overcome the above-mentioned shortcomings.